Lightweight circuit board with conductive constraining cores

ABSTRACT

Prepregs, laminates, printed wiring board structures and processes for constructing materials and printed wiring boards that enable the construction of printed wiring boards with improved thermal properties. In one embodiment, the prepregs include substrates impregnated with electrically and thermally conductive resins. In other embodiments, the prepregs have substrate materials that include carbon. In other embodiments, the prepregs include substrates impregnated with thermally conductive resins. In other embodiments, the printed wiring board structures include electrically and thermally conductive laminates that can act as ground and/or power planes.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] The present application claims priority on the basis of theprovisional patent application Serial No. 60/254,997, filed Dec. 12,2000, and entitled “LIGHTWEIGHT MULTIPLE LAYER PRINTED WIRING BOARD.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Certain portions of the background technology to the presentinvention were made under one or more of the following United StatesGovernment Contracts: NAS 3-27743; NAS 3-97040; and F 29601-94-C-0093.Accordingly, the United States Government may have some rights.

BACKGROUND OF THE INVENTION

[0003] Multiple-layer printed circuit boards or printed wiring boards(PWBs) are used for mounting integrated circuits (ICs) and othercomponents. The push to decrease circuit size and weight and to operateat higher frequencies and clock speeds has led to smaller componentsgenerating greater heat and being placed more closely together on thePWB. Additional size and speed improvements have also been achieved byreducing the footprints of the components by using leadless chipcarriers.

[0004] The greater density of components on the PWBs and hottercomponents resulted in thermal management problems. The Coefficient ofThermal Expansion (“CTE”) mismatch between the PWBs and the componentsbecomes more important when greater temperatures are generated. CTEmismatch between the PWBs and components can result in fracture orfatigue during the thermal cycling caused by powering on and off ofelectronic devices. Leadless chip carriers are especially susceptible todisengagement from the PWB when there are CTE mismatches. Solder jointsand connections tend to pull apart in the “tug-of-war” introduced by theCTE mismatch.

[0005] Prior PWB designs have used metal constraining layers or cores,such as copper-invar-copper, aluminum or steel, to lower the board'sCTE. However, these materials add undesirable weight. U.S. Pat. No.4,318,954 to Jensen provides an example of a PWB design for use incycling thermal environments that uses lightweight carbon basedconstraining layers to lower the board's CTE. U.S. Pat. No. 4,591,659 toLeibowitz also demonstrates that carbon constraining layers can serve asthermal conductors for carrying heat away from the components mounted onthe PWB in addition to lowering the board's CTE. U.S. Pat. No. 4,318,954to Jensen and U.S. Pat. No. 4,591,659 to Leibowitz are incorporated byreference in their entirety to the present disclosure.

[0006] The ability of previous PWBs to conduct heat away from thecomponents mounted on their surfaces is limited by the prepreg used toprevent electrical conductivity between the functional layers of thePWB. The materials used in prepreg have poor thermal conductionproperties. Therefore, the ability of the carbon constraining layer toconduct heat away from the surface of the board was limited by theamount of prepreg between it and the surface of the board. The carbonmaterial used in the carbon constraining layers is electricallyconductive, which required the functional layers of the PWB in priorstructures to be electrically insulated from the carbon constraininglayers in order to prevent short circuits and cross talk. In previousdesigns, this requirement places a lower limit on the distance betweenthe carbon constraining layers and the surface of the board equivalentto the minimum amount of prepreg required to insulate the functionallayers of the board from each other and from the carbon constraininglayers. This lower limit translated into an upper limit on the amount ofheat that could be conducted away from the surface of the PWB.Accordingly there was a need for a PWB that possessed mechanicalstrength with a low CTE and that exceeds the upper limit on the amountof heat that can be conducted away from the surface of the PWB which wasinherent in previous designs.

SUMMARY OF THE INVENTION

[0007] In one aspect, the invention relates to a structure and method inwhich a thermally conductive layer is provided in a PWB or a portionthereof. For example, the invention may include a prepreg layer made ofa substitute impregnated with a resin which is thermally conductive, andpossibly also electrically conductive. A laminate may be formed fromsuch a prepreg layer, the laminate having first and second metalliclayers positioned above and below the prepreg. Alternatively, thelaminate may itself be thermally and/or electrically conductive,enabling its use in a high performance printed wiring board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including an electrically andthermally conductive laminate;

[0009]FIG. 2A is a flow chart illustrating a process for constructing aPWB in accordance with the present invention;

[0010]FIG. 2B is a flow chart illustrating a process for impregnating asubstrate with resin in accordance with the present invention;

[0011]FIG. 3 is a semi-schematic cross-sectional view showing a laminateincorporating four layers of unidirectional carbon fibers;

[0012]FIG. 4 is a semi-schematic cross-sectional view showing anotherembodiment of a laminate incorporating four layers of unidirectionalcarbon fibers;

[0013]FIG. 5 is a semi-schematic cross-sectional view showing a laminateincorporating three layers of unidirectional carbon fibers;

[0014]FIG. 6 is a semi-schematic cross-sectional view showing a laminateincorporating four layers of unidirectional carbon fibers in anisotropic configuration;

[0015]FIG. 7 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including a laminate incorporatingprepreg layers;

[0016]FIG. 8 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including an electrically andthermally conductive laminate including a fiber glass layer impregnatedwith electrically and thermally conductive resin;

[0017]FIG. 9 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including an electrically andthermally conductive laminate having a fiber glass layer impregnatedwith electrically and thermally conductive resin contained within layersof prepreg;

[0018]FIG. 10 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including two electrically andthermally conductive laminates and a number of chimneys and platedthrough holes;

[0019]FIG. 11A is a flow chart illustrating a process for manufacturinga PWB in accordance with the present invention including multipleelectrically and thermally conductive laminates, chimney holes andplated through holes;

[0020]FIG. 11B is a flow chart illustrating a process for determininglocations in which to drill chimney holes in a PWB;

[0021]FIG. 11C is a flow chart illustrating a process for determininglocations in which to drill filled clearance holes in electrically andthermally conductive laminates during the construction of a PWB inaccordance with the present invention; and

[0022]FIG. 12 is a semi-schematic cross-sectional view showing a PWB inaccordance with the present invention including two electrically andthermally conductive laminates and an electrically isolated carbonsupport layer.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring now to the drawings, FIG. 1 illustrates a lightweightmultiple-layer PWB in accordance with the present invention. The PWB 10includes a laminate 12 comprising a carbon containing layer 14sandwiched between a first layer of metal or other electricallyconductive material 16 and a second layer of metal or other electricallyconductive material 18. The laminate is sandwiched between a first layerof prepreg 20 and a second layer of prepreg 22. The top layer of the PWBis constructed from a third layer of metal or other electricallyconductive material 24. The bottom layer of the PWB is constructed usinga fourth layer of metal or other electrically conductive material 26. Asset forth below, the electrically conductive layers 16, 18, 24 and 26,and the corresponding layers of the other embodiments described herein,may be made of metal or any of a variety of metal-containingcompositions having suitable properties of electrical conduction. Forconvenience, however, these layers often will be referred to hereinsimply as “metal” layers.

[0024] The laminate 12 is electrically conductive, which enables thelaminate to be used as a ground plane within the PWB, a power planewithin a PWB or both a ground and power plane in the PWB where routingis used to electrically isolate portions of the laminate. Use of thelaminate 12 in a PWB results in the PWB being thinner and having lessweight than previous PWB designs that utilize electrically insulatedcarbon containing layers to lower the CTE. Reducing the thickness of thePWB 10 also enables the carbon containing layers 14 to be located closerto the surface of the board than in PWBs that utilize electricallyinsulated carbon constraining layers. An advantage of this configurationis that it gives the PWB increased ability to transfer heat away fromits surface compared to previous designs. Another advantage of thisconfiguration is that it provides low surface CTE which is important inapplications such as semiconductor applications.

[0025] A prepreg is a composite layer that includes a substrate orsupporting material composed of fibrous material that is impregnatedwith resin. A prepreg may also be a film. A film is a type of prepregthat does not include a substrate but is instead a composite that onlyincludes resins. The first prepreg layer 20 and the second prepreg layer22 electrically insulate the electrically conductive laminate 12 fromthe third layer of metal 24 and the fourth layer of metal 26. In onepreferred embodiment, the third and fourth layers of metal or otherelectrically conductive material are patterned with electrical circuits.For example, electrical contact between the third layer of metal, theelectrically conductive laminate or the fourth layer of metal can resultin the functions of the electrical circuits patterned onto the third andfourth layers of metal being interrupted. In other embodiments, only oneof the third and fourth layers of metal are patterned with electricalcircuits.

[0026] In one preferred embodiment of the PWB in accordance with thepresent invention, the layer containing carbon used in the constructionof the laminate 12 is made from woven carbon fibers such as woven K13C2Umanufactured by Mitsubishi Chemical America, Inc. of Sunnyvale, Calif.and having a thickness of 0.006 inches. In another embodiment, the layercontaining carbon can be constructed from carbon fibers having a tensilemodulus of 110 msi, a tensile strength of 540 ksi, a thermalconductivity of 610 W/m.K, a fiber density of 2.15 g/cc and a fiberelongation of 0.5% and that are woven with a balanced weave. In otherembodiments, the layer containing carbon can be constructed from anywoven carbon fibers having a thickness greater than 0.002 inches, athermal conductivity greater than 10 W/m.K, a co-efficient of thermalexpansion in the range −3.0 to 3.0 ppm/C, a stiffness greater than 20msi, a tensile greater than 250 ksi, a density less than 2.25 gm/cc.Preferably, the layer containing carbon is constructed from woven carbonfibers having a thermal conductivity greater than 75 W/m.K, aco-efficient of thermal expansion in the range −1.25 to 1.0 ppm/C, astiffness greater than 35 msi, a tensile strength greater than 350 ksi,a density less than 2.22 gm/cc. More preferably, the layer containingcarbon is constructed from woven carbon fibers having a co-efficient ofthermal expansion of 0.0 ppm/C. In other embodiments, the layercontaining carbon is constructed from any woven carbon fibers capable ofdissipating the required amount of heat from the surface of the PWB 10,to support the CTE requirements of the PWB and to achieve the desiredstiffness of the PWB.

[0027] In one preferred embodiment, the woven carbon fibers areimpregnated with an electrically and thermally conductive resin such asan epoxy pyrolitic carbon resin in accordance with the process describedabove in relation to FIG. 2B. Electrical conductivity is defined ashaving a dielectric constant greater than 6.0 at 1 MHz. Thermalconductivity is defined as having a thermal conductivity of greater than1.25 W/m.K. Preferably, a material that is thermally conductive willhave a thermal conductivity greater than 2.5 W/m.K. In otherembodiments, the woven carbon fibers are impregnated with a resin suchas polyimide (cyanate ester) based pyrolitic carbon resin, epoxy orpolyimide based silver oxide resin, epoxy or polyimide based carbonpowder resin or any other resin having a glass transition temperaturegreater than 100° F., low moisture absorption, high resistance tochemical corrosion, high resistance to microcracking, high structuraldurability, controlled flow, good adhesion, a thermal conductivitygreater than 0.2 W/m.k and a dielectric constant greater than 6.0 at 1Mhz. Preferably, the woven carbon fibers are impregnated with a resinhaving a glass transition temperature greater than 250° F. and a thermalconductivity greater than 2.0 W/m.k.

[0028] In one preferred embodiment, the first and second layers of metalare constructed from a ¼ oz copper foil such as NT-TW-HTE manufacturedby Circuit Foil Trading, Inc of Glenside, Philadelphia. In otherembodiments, other electrically conductive materials such as Cu,Palladium, Ag, Al, Au, Ni and Sn, or alloys or other compositionsthereof, having thicknesses from 0.00003 inches to 0.021 inches can beused in the construction of the first and second layers of metal. Inother embodiments, an electrically conductive material of any thicknesscan be used in the construction of the first and second layers of metalprovided that the overall conductivity of the electrically conductivelaminate 12 is sufficient to carry the electrical load in the laminate.

[0029] In one preferred embodiment, the first prepreg layer and thesecond prepreg layer are constructed from thermally conductivedielectric material such as the prepreg 44N0680 manufactured by ArlonMaterials for Electronics of Rancho Cucamonga, California having athickness of 0.0015 inches, a resin content of approximately 80%, aresin flow of approximately 50% and a gel time in the range of 90 to 110seconds. In other embodiments, other prepregs such as FR-4, polyimide,teflon, ceramics, GIL, Gtek or high frequency circuit materialsmanufactured by Rogers Corporation that include additives such asaluminum oxide, diamond particles or boron nitride or any other prepreghaving dielectric constants less than 6.0 at 1 MHz and a thermalconductivity of greater than 1.25 W/m.K can be used in the constructionof the first and second prepreg layers. More preferably, the first andsecond prepreg layers are constructed from a dielectric material havinga dielectric constant less 4.0 at 1 Mhz and a thermal conductivitygreater than 2.0 W/m.K. In other embodiments, prepregs that have thermalconductivity less than 1.25 W/m.K can be used in the construction of thefirst and second prepreg layers. Use of prepreg layers that have athermal conductivity that is less than 1.25 W/m.K can reduce the abilityof the PWB to conduct heat away from its surface.

[0030] In one preferred embodiment the top and bottom layers ofconductive material are constructed from materials similar to those usedin the construction of the first and second layers of metal as describedabove.

[0031] One preferred embodiment of a method of manufacturing PWBs inaccordance with the present invention is illustrated in FIG. 2A. A firstlamination is performed in the step 32. The first lamination involvesplacing a ¼ oz layer of copper foil on one side of a layer of wovencarbon fibers impregnated with the epoxy based pyrolitic carbon resin,as described above, and placing a second ¼ oz layer of copper foil onthe other side of the layer of woven carbon fibers. The layers are thenplaced in a vacuum and heated from room temperature to 350° F. Thetemperature increase is controlled so that the temperature rise ismaintained within the range of 8-12° F./min as the temperature risesfrom 150° F. to 300° F. When the temperature is in the range 150°F.-165° F., the pressure on the layers is increased to 250 PSI. Once atemperature of 350° F. has been reached, the temperature is maintainedat that temperature for 70 minutes. After the completion of the 70minute time period, the layers are exposed to room temperature and apressure greater than atmospheric pressure for a period of 30 minutes.The first lamination cycle produces the electrically conductive laminate12 described above. Preferably, the electrically conductive laminate ismanufactured to be as flat as possible.

[0032] The first lamination cycle is followed by a second laminationcycle in the step 34. The second lamination cycle involves placing alayer 44N0680 prepreg on one side of the electrically conductivelaminate produced in the first lamination cycle and a second layer of44N0680 prepreg on the other side of the electrically conductivelaminate. In addition, layers of ½ oz copper foil are placed on theoutside surfaces of the two layers of 44N0680 prepreg. The layers arethen placed in a vacuum and heated from room temperature to 350° F. Thetemperature increase is controlled so that the temperature rise ismaintained within the range of 8-12° F./min as the temperature risesfrom 150° F. to 300° F. When the temperature is in the range 150°F.-165° F., the pressure on the layers is increased to 250 PSI. Once atemperature of 350° F. has been reached, the temperature is maintainedat that temperature for 90 minutes. After the completion of the 90minute time period, the layers are exposed to room temperature and apressure greater than atmospheric pressure for a period of 30 minutes.The first lamination cycle produces the electrically conductive laminate12 described above. The second lamination cycle produces the PWB 10shown in FIG. 1. The third and fourth layers of metal of the PWB 10shown in FIG. 1 are then patterned with electrical circuits in the step36.

[0033] One preferred embodiment of a process 40 for impregnating a layercontaining carbon constructed from woven carbon fiber with anelectrically conductive resin is illustrated in FIG. 2B. The first stepin the process 42 involves adding together ingredients to form a resin.Most resins are formed using epoxy or polyimide solid state resin,solvent, acetones, catalysts and additives. Typically, the properties ofa particular resin are determined by the various additives included inthe resin and the quantities of these additives. Additives can be usedto increase the electrical conductivity or the thermal properties of aresin. When an additive is used to increase the electrical or thermalconductivity of a resin, the thermal or electrical conductivity of aresin increases with the amount of the additive mixed through the resin.In one preferred embodiment, an amount of pyrolitic carbon in powderform equal to 10% by weight of the resin is added as an ingredient toincrease the electrical conductivity and thermal properties of theresin. In other embodiments, any amount of pyrolitic carbon can be addedto improve the thermal and electrical properties of the resin.Preferably, the amount of pyrolitic carbon added to the resin is between5% to 50% by weight of the resin. The various resin ingredients are thenmixed in the step 44 to form a substantially homogenous resin.

[0034] Once a resin is formed, the resin is placed in a prepreg treaterin the step 46. The prepreg treater is used to impregnate a substratewith resin. In the next step 48, the substrate to be impregnated ispassed through the prepreg treater. In one preferred embodiment of theprocess, the substrate material is woven carbon fibers such as the wovencarbon fiber materials described above. In one preferred embodimentusing a woven carbon fiber substrate, the substrate is impregnated with45% by weight resin. In other embodiments, the substrate is impregnatedwith between 5% to 80% by weight resin.

[0035] Once the substrate has been passed through the prepreg treater,the B-stage curing cycle is performed in the step 50. The B-stage curingcycle involves exposing the substrate and resin to a temperature ofbetween 250° F. to 300° F. The amount of time that the substrate andresin are exposed to this temperature is determined by the amount ofresin loaded onto the substrate and the extent of curing required. Inone preferred embodiment, a time period of 15 minutes is required forthe impregnation of a woven carbon fiber substrate with 45% resin curedto B-stage so that it is suitable for use in the process described abovein relation to FIG. 2A. Upon the completion of the B-stage curing cycle,the resin is stored in a controlled environment prior to use in the step52.

[0036] In other embodiments, silver oxide particles are used as a resinadditive to increase the electrical conductivity and thermal propertiesof the resin. In one preferred embodiment, an amount of silver oxideequal to 40% by weight of the resin is added. In other embodiments, anyamount of silver oxide can be added to increase the thermal propertiesof the resin. Preferably, the amount of silver oxide added to the resinwill be between 5% and 70% by weight of the resin.

[0037] In other embodiments, boron nitride particles are used as a resinadditive to increase the thermal properties of the resin. In onepreferred embodiment, an amount of boron nitride equal to 40% by weightof the resin is added. In other embodiments, any amount of boron nitridecan be added to increase the thermal properties of the resin.Preferably, the amount of boron nitride added to the resin will bebetween 5% and 70% by weight of the resin.

[0038] In other embodiments, diamond particles are used as a resinadditive to increase the thermal properties of the resin. In onepreferred embodiment, an amount of diamond particles equal to 15% byweight of the resin is added. In other embodiments, any amount ofdiamond particles can be added to increase the thermal properties of theresin. Preferably, the amount of diamond particles added to the resinwill be between 2% to 50% by weight of the resin.

[0039] In other embodiments, aluminum oxide particles are used as aresin additive to increase the thermal properties of the resin. In onepreferred embodiment, an amount of aluminum oxide equal to 40% by weightof the resin is added. In other embodiments, any amount of aluminumoxide can be added to increase the thermal properties of the resin.Preferably, the amount of aluminum oxide added to the resin will bebetween 5% to 70% by weight of the resin. In other embodiments, two ormore of the additives described above can be used as additives to form aresin.

[0040] In other embodiments, prepregs can be manufactured using theabove process by using substrate materials that have dielectricconstants less than 6.0 at 1 MHz. In one preferred embodiment, afiberglass substrate is impregnated with a resin containing boronnitride to produce a thermally conductive prepreg with a dielectricconstant less than 6.0 at 1 MHz. Preferably, the fiberglass isimpregnated with 70% by weight resin. In other embodiments, thefiberglass is impregnated with between 20% and 80% by weight resin.

[0041] In other embodiments, other substrates such as kevlar, quart,aramid or any other material or mixture of materials having a dielectricconstant less than 6.0 at 1 MHz, a glass transition temperature greaterthan 250° F., a thermal conductivity greater than 0.1 W/m.K, a CTEbetween −4.5 ppm/° C. and 30 ppm/° C., high tensile strength and highthermal endurance can be used in the construction of prepreg layers.Preferably, the substrate material has a glass transition temperaturegreater than 400° F., a CTE between −4.5 ppm/° C. and 12 ppm/° C.,retains 50% to 60% of its strength at 700° F. and has a dielectricconstant less than 3.0 at 1 Mhz. Prepreg manufactured using this processcan be used in the construction of the first and second prepreg layersof the PWB 10 in accordance with the present invention illustrated inFIG. 1.

[0042] In other embodiments, the layer containing carbon is impregnatedwith a resin that is thermally conductive such as a epoxy or polyimidebased boron nitride resin, epoxy or polyimide based aluminum oxide,epoxy or polyimide based ceramic resin, epoxy or polyimide based diamondparticles resin or any other resin having properties similar to theelectrically and thermally conductive resins described above except thatthe dielectric constant of the resin is less than 6.0 at 1 Mhz.

[0043] In other embodiments, the layer containing carbon is constructedfrom a sheet of unidirectional carbon fiber such as unidirectionalK13C2U manufactured by Mitsubishi Chemical America, Inc. and having athickness of 0.001 inches. The unidirectional carbon fiber materialchosen for use in the construction of the carbon containing layerpreferably has properties similar to those described above for the wovencarbon fiber that can be used in the construction of the layercontaining carbon.

[0044] In other embodiments, the sheet of unidirectional carbon fiber isimpregnated with resin. Resins with similar properties to thosedescribed above in relation to embodiments of laminates incorporatingsheets of woven carbon fiber can also be used to impregnate sheets ofunidirectional carbon fiber used in the construction of laminates inaccordance with the present invention.

[0045] In other embodiments, multiple layers of unidirectional carbonfiber that are aligned such that the fibers in each of the layers aresubstantially parallel can be used in the construction of the layercontaining carbon.

[0046] One preferred embodiment of a laminate 12′ constructed inaccordance with the present invention using four unidirectional layersof carbon fiber is illustrated in FIG. 3. In this embodiment, thelaminate is constructed from a first unidirectional layer of carbonfiber 60, a second unidirectional layer of carbon fiber 62, a thirdunidirectional layer of carbon fiber 64 and a fourth unidirectionallayer of carbon fiber 66. Each of the unidirectional layers of carbonfiber have the same thickness and fiber area weight. The first andfourth unidirectional layers of carbon fiber are constructed so that thecarbon fibers in each layer are aligned to be substantially parallel.The second and third unidirectional layers of carbon fiber areconstructed from sheets of unidirectional carbon fiber, where the fibersare aligned substantially perpendicular to the carbon fibers in thefirst and fourth layers.

[0047] Another preferred embodiment of a laminate 12″ constructed inaccordance with the present invention using unidirectional layers ofcarbon fiber are illustrated in FIG. 4. In this embodiment the laminate12″ is constructed from a first unidirectional layer of carbon fiber 70,a second unidirectional layer of carbon fiber 72, a third unidirectionallayer of carbon fiber 74 and a fourth unidirectional layer of carbonfiber 76. Each of the unidirectional layers of carbon fiber have thesame thickness and fiber area weight. The first and third unidirectionallayers of carbon fiber are constructed from sheets of unidirectionalcarbon fiber having fibers aligned in substantially the same direction.The second and fourth unidirectional layers of carbon fiber areconstructed from sheets of unidirectional carbon having fibers alignedin a direction substantially perpendicular to the direction in which thefibers in the first and third unidirectional layers of carbon fiber arealigned.

[0048] Another preferred embodiment of a laminate 12′″ constructed inaccordance with the present invention using unidirectional layers ofcarbon fiber are illustrated in FIG. 5. In this embodiment the laminate12′″ is constructed from a first unidirectional layer of carbon fiber 80having a thickness of 0.002 inches, a second unidirectional layer ofcarbon fiber 82 having a thickness of 0.004 inches and a thirdunidirectional layer of carbon fiber 84 having a thickness of 0.002inches. The fiber area weight of the first and third unidirectionallayers of carbon fiber have the same fiber area weight, which is halfthe fiber area weight of the second unidirectional layer of carbonfiber. The first and third unidirectional layers of carbon fiber areconstructed from sheets of unidirectional carbon fiber having fibersaligned in the same direction. The second unidirectional layer of carbonfiber is constructed from a sheet of unidirectional carbon having fibersaligned in a direction perpendicular to the direction in which thefibers in the first and third unidirectional layers of carbon fiber arealigned.

[0049] In other embodiments, a number of layers of unidirectional carbonfiber greater than four can be used in the construction of the printedcircuit board provided that the layer containing carbon fiber isbalanced.

[0050] In other embodiments, laminates in accordance with the presentinvention include layers containing carbon that are substantiallyisotropic. One embodiment of a laminate in accordance with the presentinvention incorporating an isotropic carbon containing layer isillustrated in FIG. 6. The laminate 12″″ includes a first unidirectionallayer of carbon fiber 90 constructed from a sheet of unidirectionalcarbon fiber with fibers aligned in a first reference direction, asecond unidirectional layer of carbon fiber 92 constructed from a sheetof unidirectional carbon fiber positioned so that its fibers are alignedat an angle of 45° to the first reference direction, a thirdunidirectional layer of carbon fiber 94 constructed from a sheet ofunidirectional carbon fiber positioned so that its fibers are aligned atan angle of 90° to the first reference direction and a fourthunidirectional layer of carbon fiber 96 constructed from a sheet ofunidirectional carbon fiber positioned so that its fibers are aligned atan angle of 135° to the first reference direction. The sheets ofunidirectional carbon fiber can be impregnated with resins similar tothose resins described above.

[0051] A PWB in accordance with the present invention is illustrated inFIG. 7. The PWB 10′ includes a laminate structure 12′″″ having a carboncontaining layer 14′ positioned between a first layer of prepreg 100 anda second layer of prepreg 102. A first layer of metal 16′ is positionedabove the first prepreg layer and a second layer of metal 18′ ispositioned beneath the second prepreg layer. A third layer of prepreg20′ is positioned above the first layer of metal and a second layer ofprepreg 22′ is positioned below the second layer of metal. A third layerof metal 24′ is positioned above the third layer of prepreg and a fourthlayer of metal 26′ is positioned below a fourth layer of prepreg.

[0052] In one preferred embodiment, the layer containing carbon 14′ isconstructed from a woven sheet of carbon fiber and the layers of metalare constructed from materials similar to those described above in theconstruction of the layers of metal used in the construction of theembodiment of the PWB shown as 10 in FIG. 1. In addition, third andfourth prepreg layers are constructed from materials similar to thosedescribed above in the construction of the first and second prepreglayers of the embodiment of the PWB shown as 10 in FIG. 1.

[0053] In one preferred embodiment an electrically and thermallyconductive prepreg layer such as epoxy based pyrolitic carbon resinprepreg manufactured in accordance with the process described above inrelation to FIG. 2B, and having properties similar to the pyroliticcarbon resin described above, is used in the construction of the firstand second prepreg layers. An electrically and thermally conductiveprepreg is used in the construction of the first and second prepreglayers to ensure that an electrically conductive path exists between thelayer containing carbon and the first and second electrically conductivelayers. In other embodiments, other electrically and thermallyconductive prepregs such as polyimide based pyrolitic carbon resinprepreg, epoxy or polyimide based silver oxide resin prepreg or anyother prepreg having a glass transition temperature greater than 100°F., low moisture absorption, high resistance to chemical corrosion, highresistance to micro cracking, high structural durability, controlledflow, good adhesion, a thermal conductivity greater than 0.2 W/m.k and adielectric constant greater than 6.0 at 1 Mhz can be used in theconstruction of the first and second prepreg layers. Preferably, thefirst and second prepreg layers are constructed from a prepreg having aglass transition temperature greater than 250° F. and a thermalconductivity greater than 2.0 W/m.k.

[0054] The method of manufacturing the PWB 10′ illustrated in FIG. 7 issimilar to the method illustrated in FIG. 2A. A layer of epoxy basedpyrolitic carbon resin prepreg is placed on one side of a layer of wovencarbon fibers and a second layer of epoxy based pyrolitic carbon resinprepreg is placed on the other side of the layer of woven carbon fiber.Layers of ¼ oz copper foil are then placed on the outside surfaces ofthe layers of epoxy based pyrolitic carbon resin prepreg. These layersare then subjected to the first lamination cycle as described above inrelation to FIG. 2A to produce the laminate 12′″″. The second laminationcycle and the patterning of the PWB 10′ are also similar to processesdescribed above in relation to FIG. 2A.

[0055] In other embodiments, thermally conductive prepreg layers similarto those used in the construction of the first and second prepreg layersof the embodiment of the PWB 10 shown in FIG. 1, as described above, canbe used in the construction of the first and second prepreg layers ofthe embodiment of the PWB 10′ shown in FIG. 7. In embodiments of the PWB10′ that use thermally conductive prepreg layers that are poorconductors of electricity, electrical contacts are made between thefirst and second layers of metal and the carbon containing layer byplated through holes. Plated through holes are holes drilled through thelaminate 12′″″ that are lined with electrically conductive material andestablish electrical contacts between the first and second layers ofmetal and the layer containing carbon.

[0056] In other embodiments, the laminate 12′″″ is constructed from alayer containing carbon made from layers of unidirectional carbon fibersthat have arrangements similar to the arrangements described above inrelation to the embodiments of laminates in accordance with the presentinvention illustrated in FIGS. 3-6. In other embodiments, the layers ofunidirectional carbon fibers are impregnated with resins similar tothose described above prior to the construction of the laminate 12′″″.

[0057] In other embodiments, the laminate 12′″″ is constructed from alayer containing carbon that is made from a carbon composite sheet orplate such as a carbon plate manufactured by Mitsubishi ChemicalAmerica, Inc having a thickness of 0.001 inches. A carbon compositesheet or plate can be constructed using a compressed powder mold. Inother embodiments, the layer containing carbon can be constructed fromany carbon composite sheet or plate has physical properties similar tothose described above in relation to woven carbon fiber.

[0058] For embodiments of the laminate 12′″″ constructed using layerscontaining carbon made from carbon composite sheets or plates, the firstlayer of prepreg 100 and the second layer of prepreg 102 can beconstructed from resins similar to those described above.

[0059] A PCB in accordance with the present invention is illustrated inFIG. 8. The PCB 10″ includes an electrically and thermally conductivelayer 110. A first layer of metal 16″ is positioned above theelectrically and thermally conductive layer and a second layer of metal18″ is positioned below the electrically and thermally conductive layer.A first prepreg layer 20″ is positioned above the first layer of metaland a second prepreg layer 22″ is positioned below the second layer ofmetal. A third layer of metal 24″ is positioned above the first prepreglayer and a fourth layer of metal 26″ is positioned below the secondprepreg layer. The electrically and thermally conductive layer and thefirst and second layers of metal form an electrically conductivelaminate 112.

[0060] In one preferred embodiment, similar materials to those that canbe used in the construction of the embodiment of the PWB 10 inaccordance with the present invention illustrated in FIG. 1 can also beused in the construction of the first and second prepreg layers and thefirst, second, third and fourth layers of metal. In one preferredembodiment, the third and fourth layers of metal are patterned tocontain electrical circuits.

[0061] In one preferred embodiment, the electrically and thermallyconductive layer is constructed from a woven fiberglass substrateimpregnated with an electrically conductive epoxy pyrolitic carbon resinin accordance with the process described above in relation to FIG. 2B.Preferably, the woven fiberglass used in the construction of theelectrically and thermally conductive layer is E-glass manufactured byJPS Glass located at South Cickering of Ontario in Canada. In otherembodiments, other substrate materials such as non-woven fiberglass,kevlar, quartz, aramid or other materials having a glass transitiontemperature greater than 250° F., a thermal conductivity greater than0.1 W/m.K, a CTE between −4.5 ppm/° C. and 30 ppm/° C., high tensilestrength and high thermal endurance. Preferably, the substrate has aglass transition temperature greater than 400° F., a CTE between −4.5ppm/° C. and 12 ppm/° C., retains 50% to 60% of its strength at 700° F.Preferably, the fiberglass substrate is impregnated with 70% by weightresin of an epoxy resin containing 10% by weight pyrolitic carbonadditive. In other embodiments, the electrically and thermallyconductive layer is formed using a substrate that is impregnated withbetween 5% to 80% of any of the resins described above having adielectric constant greater than 6.0 at 1 MHz. In other embodiments, anyresin and substrate combination can be used that results in theelectrically and thermally conductive layer 14′ having a dielectricconstant greater than 6.0 at 1 Mhz.

[0062] The embodiment of the PWB 10″ illustrated in FIG. 8 can bemanufactured in accordance with the processes illustrated in FIG. 2A andFIG. 2B.

[0063] An embodiment of a PWB in accordance with the present inventionis illustrated in FIG. 9. The PWB 10′″ is similar to the PWB 10′illustrated in FIG. 7 except that the carbon containing layer isreplaced with any of the substrate materials described above and thatthe first and second prepreg layers possess dielectric constants greaterthan 6.0 at 1 MHz.

[0064] The embodiments of PWBs described above have utilized a singlelaminate. In other embodiments of PWBs in accordance with the presentinvention, multiple laminates can be used.

[0065] A PWB in accordance with the present invention including twolaminates is illustrated in FIG. 10. The PWB 10″″ includes a firstlaminate 120, a second laminate 122, multiple layers of prepreg 124 andmultiple layers of metal 126. In one preferred embodiment, the firstlaminate forms a ground plane and the second laminate forms a powerplane. In other embodiments, the function of the laminates can bereversed, both laminates can share the same functions or the laminatescan be utilized for their improved thermal properties only. The use ofmultiple laminates can increase the ability of the PWB to conduct heataway from its surface, improve the CTE of the PWB and can decrease thethickness and weight of the PWB, when compared to prior art PWBs.

[0066] In one preferred embodiment, the first laminate 120 and secondlaminate 122 are constructed similarly to the laminate 12 of FIG. 1. Inother embodiments any of the laminate structures described above can beused in the construction of the first or second laminate. Preferably,the layers of prepreg 124 and layers of metal are constructed frommaterials similar to those that can be used to construct the prepreglayers and the layers of metal in the PWB 10 illustrated in FIG. 1. Inother embodiments any of the laminates described above can be used inthe construction of the first and second laminates.

[0067] A closer inspection of FIG. 10 reveals that the PWB 10″″ includesa number of plated holes. The PWB 10″″ includes chimneys 128 that areholes filled with thermally conductive material. The chimneys are usedto transport heat from the surface of the PWB to the electrically andthermally conductive laminates within the PWB. The chimneys do notextend all the way through the PWB. If the chimneys contacted both thefirst and second laminates, then the chimneys could short circuit thePWB. The PWB 10″″ also includes through holes 130 lined withelectrically conductive material that are used to establish electricalconnections between the functional layers in the PWB. Where connectionsbetween the plated through holes and the first or second laminates arenot desired, then an annulus of dielectric material 132 such as an epoxyresin with a dielectric constant less than 6.0 at 1 MHz can be used toensure that an electrical connection does not exist between the laminateand the electrically conductive lining of the through hole.

[0068] A process in accordance with the present invention formanufacturing the PWB 10″″ illustrated in FIG. 10 is shown in FIG. 11A.The process 150 commences with the step 152, which involves constructingtwo laminates in accordance with the present invention are formed usingthe process described above in relation to FIG. 2A. Power or groundregions are then patterned on the laminates in the step 154. Thepatterning electrically isolates regions within the laminate, which canenable laminate to function as a ground or power plane within a PWB.

[0069] Once the patterning is complete, the laminates are subjected tooxide treatment in the step 156. After oxide treatment, clearance holedrilling is performed in the step 158. Clearance hole drilling involvesdrilling holes in the laminate of a first diameter and filling theresulting holes with a dielectric material such as any of the resinsdescribed above with a dielectric constant less than 6.0 at 1 MHz. Priorto filling the drilled holes, they are inspected and cleaned using highpressure dry air.

[0070] Once the clearance holes have been drilled, the second laminationcycle is performed in the step 160. The second lamination cycle issimilar to the second lamination cycle described above in relation toFIG. 2A. After the second lamination cycle, chimney holes are drilledinto the PWB in the step 162. Once the chimney holes have been drilled,the linings of the chimney holes are lined with a thermally conductivematerial in the step 164. Preferably, the thermally conductive materialis copper. In other embodiments, any material with a thermalconductivity greater than 5 W/m.K can be used.

[0071] After the chimney holes have been lined, circuits are etched ontothe layers of metal that will be located within the interior of thefinished PWB are patterned in the step 166 and then subjected to oxidetreatment in the step 168.

[0072] Following the oxide treatment, the third lamination is performedin the step 170. The third lamination involves aligning the twostructures produced in the second lamination with additional prepreglayers to correspond with the layers of the PWB 10″″ illustrated in FIG.10. The layers are then exposed to temperatures and pressures similar tothose experienced during the second lamination cycle.

[0073] After the third lamination cycle, the final through hole drillingis performed in step 172. The final through hole drilling involvesdrilling holes through the entire PWB that have a second diameter, whichis less than the first diameter described above. The through holes arethen lined in the step 174. Preferably, the through holes are lined withcopper. In other embodiments, the through holes can be plated withmaterials similar to those that can be used in the construction of thelayers of metal. If a through hole passes through one of the filledclearance holes in a laminate, then the lining of the through holes areelectrically isolated from the laminate in which the clearance hole isdrilled. If a through hole does not pass through one of the filledclearance holes in a laminate, then the lining of the through hole is inelectrical contact with the laminate.

[0074] An embodiment of a process for selecting the locations in whichto drill chimney holes in a PWB is illustrated in FIG. 11B. The process190 includes a first step 192, which involves creating a model of thestructure of the PWB. The second step 194 involves adding a thermallyconductive material such as copper to the outermost layers of metal onthe model. The thermally conductive material is added to the model suchthat the thermally conductive material does not create any electricalcontacts with the circuits patterned onto the layers of metal on whichthe thermally conductive material is added.

[0075] Once the thermally conductive material has been added, thelocations of the chimney holes are determined in the step 196. Thelocations of the chimney holes are determined by choosing a location onthe surface of the PWB that lies within an area where thermallyconductive material was added during step 194. The location is asuitable location for a chimney if a hole of a specified diametercorresponding to the diameter of the chimney can be drilled through thePWB without intersecting any of the electrical circuits patterned ontolayers of metal internal to the PWB. Otherwise, the chosen location isunsuitable as a location for drilling a chimney hole. The number oflocations that must be found is dependent upon the amount of heatrequired to be conducted away from the surface of the board.

[0076] An embodiment of a process for selecting the location of thefilled clearance holes in the laminates is illustrated in FIG. 11C. Theprocess 200 includes a first step 202, which involves constructing amodel of the PWB. The locations of the through holes in the PWB are usedto determine the locations in which the through holes intersect theground plane laminate or the power plane laminate in the step 204. Oncethese locations have been determined, the locations of the clearanceholes are chosen in the step 206 as the locations where the throughholes intersect the ground or power plane laminates and where anelectrical connection between the lining of the plated through hole andthe ground or power plane laminate is undesirable.

[0077] A PWB in accordance with the present invention incorporatinglaminates in accordance with the present invention and an additionalcarbon containing layer is illustrated in FIG. 12. The PWB 10′″″ has afirst laminate 120′, a second laminate 122′, an additional carboncontaining layer 210, prepreg layers 124′ and layers of metal 126′.Preferably, the first laminate forms a ground plane and the secondlaminate forms a power plane. The additional carbon containing layer210, does not act as a ground or power plane and is electricallyisolated from the laminates and the layers of metal. The additionalcarbon containing layer increases the thermal conductivity and stiffnessof the PWB and improves the CTE of the PWB. Similar materials to thoseused in the construction of the laminates, prepreg layers and layers ofmetal of the PWB 10 illustrated in FIG. 1 can also be used to constructthe laminates, prepreg layers and layers of metal of the PWB 10′″″illustrated in FIG. 12. The additional carbon containing layer can beconstructed using the similar materials to those that can be used in theconstruction of the carbon containing layers of the laminatesillustrated at 12 in FIG. 1, 12′ in FIG. 3, 12″ in FIG. 4, 12′″ in FIGS.5 and 12″″ in FIG. 6.

[0078] The PWB 10′″″ in FIG. 12 can be constructed using a processessimilar to those described above in relation to FIGS. 11A-11C. The onlydifference is in the arrangement of the materials used in theconstruction of the third lamination cycle and the fact that filledclearance holes must also be drilled in the additional carbon containinglayer 210 so that the additional carbon containing layer is electricallyisolated from the linings of any through holes present in the PWB.

[0079] Although the embodiments described above have included a singleor two laminates in accordance with the present invention, one skilledin the art would appreciate that a PWB can be constructed includingthree or more laminates using the processes described above.

What is claimed is:
 1. A prepreg, comprising a substrate impregnatedwith a thermally conductive resin.
 2. The prepreg of claim 1, whereinthe substrate material includes carbon.
 3. The prepreg of claim 2,wherein the substrate contains woven carbon fibers.
 4. The prepreg ofclaim 2, wherein the substrate includes unidirectional carbon fibers. 5.The prepreg of claim 1, wherein the substrate includes fiberglass. 6.The prepreg of claim 1, wherein the substrate includes kevlar.
 7. Theprepreg of claim 1, wherein the substrate includes aramid.
 8. Theprepreg of claim 1, wherein the substrate includes quartz.
 9. Theprepreg of claim 1, wherein the thermally conductive resin contains aboron nitride additive.
 10. The prepreg of claim 1, wherein thethermally conductive resin contains a diamond powder additive.
 11. Theprepreg of claim 1, wherein the thermally conductive resin contains analuminum oxide additive.
 12. The prepreg of claim 1, wherein thethermally conductive resin has a thermal conductivity in excess of 1.25W/m.K.
 13. The prepreg of claim 12, wherein the thermally conductiveresin has a thermal conductivity in excess of 2.5 W/m.K.
 14. The prepregof claim 1, wherein the thermally conductive resin is also electricallyconductive.
 15. The prepreg of claim 14, wherein the prepreg has adielectric constant greater than 6.0 at 1 MHz.
 16. The prepreg of claim14, wherein the electrically and thermally conductive resin contains apyrolitic carbon additive.
 17. The prepreg of claim 14, wherein theelectrically and thermally conductive resin contains a silver oxideadditive.
 18. The prepreg of claim 14, wherein the electrically andthermally conductive resin contains carbon powder as an additive. 19.The prepreg of claim 14, wherein the electrically and thermallyconductive resin has a dielectric constant greater than 6.0 at 1 MHz.20. A laminate, comprising: a prepreg, comprising a substrateimpregnated with a thermally conductive resin; a first layer ofelectrically conductive material positioned above the prepreg; and asecond layer of electrically conductive material positioned below theprepreg.
 21. The laminate of claim 20, wherein the thermally conductiveresin has a thermal conductivity in excess of 1.25 W/m.K.
 22. Thelaminate of claim 21, wherein the thermally conductive resin has athermal conductivity in excess of 2.5 W/m.K.
 23. The laminate of claim20, wherein the thermally conductive resin is also electricallyconductive.
 24. The laminate of claim 23, wherein the electrically andthermally conductive resin has a dielectric constant greater than 6.0 at1 MHz.
 25. A laminate, comprising: a substrate; a first prepreg layerpositioned above the substrate; a second prepreg layer positioned belowthe substrate; a first layer of electrically conductive materialpositioned above the first prepreg layer; and a second layer ofelectrically conductive material positioned below the second prepreglayer; and wherein the dielectric constant of the laminate is greaterthan 6.0 at 1 MHz.
 26. The laminate of claim 25, wherein the prepregscontain electrically and thermally conductive resin.
 27. The laminate ofclaim 26, wherein the prepreg has a dielectric constant greater than 6.0at 1 MHz.
 28. The laminate of claim 26, wherein the electrically andthermally conductive resin has a dielectric constant greater than 6.0 at1 MHz.
 29. A printed wiring board, comprising: an electrically andthermally conductive laminate; a first dielectric layer positioned abovethe electrically and thermally conductive laminate; and a seconddielectric layer positioned below the electrically and thermallyconductive laminate.
 30. The printed wiring board of claim 29, wherein:the electrically and thermally conductive laminate has a dielectricconstant greater than 6.0 at 1 MHz; and the first and second prepreglayers have dielectric constants less than 6.0 at 1 MHz.
 31. The printedwiring board of claim 29, wherein: the electrically and thermallyconductive laminate is configured to carry an electrical load sufficientfor the laminate to act as a ground plane in the printed wiring board.32. The printed wiring board of claim 29, wherein: the electrically andthermally conductive laminate is configured to carry an electrical loadsufficient for the laminate to act as a power plane in the printedwiring board.
 33. The printed wiring board of claim 29, wherein: theelectrically and thermally conductive laminate is partitioned such thata first portion of the electrically and thermally conductive laminate isconfigured to carry an electrical load sufficient for the first portionto act as a power plane in the printed wiring board and a second portionof the electrically and thermally conductive laminate is configured tocarry an electrical load sufficient for the second portion to act as aground plane in the printed wiring board.
 34. The printed wiring boardof claim 29, wherein: the electrically and thermally conductive laminatecomprises: a prepreg, comprising a substrate impregnated with anelectrically or thermally conductive resin; a first layer ofelectrically conductive material positioned above the prepreg; and asecond layer of electrically conductive material positioned below theprepreg.
 35. The printed wiring board of claim 29, wherein: theelectrically and thermally conductive laminate comprises: a substrate; afirst prepreg layer positioned above the substrate; a second prepreglayer positioned below the substrate; a first layer of electricallyconductive material positioned above the first prepreg layer; and asecond layer of electrically conductive material positioned below thesecond prepreg layer; and wherein the dielectric constant of thelaminate is greater than 6.0 at 1 MHz.
 36. The printed wiring board ofclaim 29, also comprising: at least one additional prepreg layer; atleast one additional layer of electrically conductive material; whereinthe electrically and thermally conducting laminate, the additionalprepreg layers and the additional layers of electrically conductivematerial are positioned adjacent each other; wherein at least oneprepreg layer is located between each of the additional layers ofelectrically conductive material; and wherein at least one prepreg layeris located between each of the additional layers of electricallyconductive material and the electrically and thermally conductinglaminate.
 37. The printed wiring board of claim 36, also comprising: atleast one additional electrically and thermally conducting laminate;wherein at least one prepreg layer is located between each of theadditional layers of electrically conductive material and the additionalelectrically and thermally conductive laminates; and wherein at leastone prepreg layer is located between each of the electrically andthermally conductive laminates.
 38. The printed wiring board of claim37, also comprising: at least one layer containing carbon; wherein atleast one prepreg layer is located between each of the additional layersof electrically conductive material and the layers containing carbon;and wherein at least one prepreg layer is located between theelectrically and thermally conductive laminates and the layerscontaining carbon.
 39. The printed wiring board of claim 29, wherein theprinted wiring board includes a plurality of lined holes that extendfrom a surface of the printed wiring board through the electrically andthermally conductive laminate.
 40. The printed wiring board of claim 39,wherein the lining of the lined holes is a thermally conductivematerial.
 41. The printed wiring board of claim 40, wherein the liningof the lined holes has a thermal conductivity greater than 1.25 W/m.K.42. The printed wiring board of claim 41, wherein the lining of thelined holes has a thermal conductivity greater than 2.5 W/m.K.
 43. Theprinted wiring board of claim 39, wherein the lining of the lined holesis an electrically and thermally conductive material.
 44. The printedwiring board of claim 43, wherein the lining of the lined holes iscopper.
 45. The printed wiring board of claim 37, wherein: theelectrically and thermally conductive laminate also comprises: aplurality of through holes extending through said printed wiring boardfor providing electrical connection between at least two of said layers;an electrically conductive lining within the through holes; and at leastone annulus of dielectric material disposed at preselected locationsbetween the electrically conductive lining and the electrically andthermally conductive laminate.
 46. The printed wiring board of claim 45,where the annuli are constructed from material having a dielectricconstant less than 6.0 at 1 MHz.
 47. The printed wiring board of claim46, where the annuli are constructed from material having a dielectricconstant less than 4.0 at 1 MHz.
 48. The printed wiring board of claim45, wherein the annuli prevent undesired electrical contact between thelinings of the through holes and the electrically and thermallyconductive laminates.
 49. A method of constructing a printed wiringboard having circuits patterned onto its outer surfaces and circuitspatterned on interior layers of conductive material, comprising thesteps of: constructing a model of the printed wiring board; determiningportions of the outer surface of the printed wiring board that do notcontain patterned circuits; determining drilling locations within saiddetermined portions that do not result in undesired electricalconnections with the circuits patterned on the interior layers of theprinted wiring board; constructing the printed wiring board such thatsaid determined portions are plated with thermally conductive material;drilling holes in the constructed printed wiring board in saiddetermined drilling locations; and lining said holes with thermallyconductive material.
 50. A method of constructing a printed wiring boardhaving an electrically and thermally conductive laminate, a plurality oflayers of electrically conductive material that have circuits patternedon them and lined through holes that connect the circuits on the layersof electrically conductive material, comprising the steps of:constructing a model of the printed wiring board; constructing saidelectrically and thermally conductive laminate; identifying thelocations in which the lined through holes intersect the electricallyand thermally conductive laminate; determining whether an electricalconnection is desired between the lining of the lined through hole andthe electrically and thermally conductive laminate at each of saidlocations; if an electrical connection is not desired at said location,then drilling a hole at said location in said electrically and thermallyconductive laminate and filling said hole with a dielectric material.51. A method of constructing a prepreg, comprising the steps of:impregnating a substrate with a thermally conductive resin.
 52. Themethod of claim 51, wherein the thermally conductive resin is alsoelectrically conductive.
 53. A method of constructing a laminate,comprising the steps of: impregnating a substrate with a thermallyconductive resin to create a prepreg having a top surface and a bottomsurface; and laminating a first layer of electrically conductivematerial to the upper surface of the prepreg and a second layer ofelectrically conductive material to the lower surface of the prepreg.54. The method of claim 53, wherein the thermally conductive resin isalso electrically conductive.
 55. A method of constructing a printedwiring board, comprising the steps of: constructing an electrically andthermally conductive laminate having an upper surface and a lowersurface; laminating a first prepreg layer to the upper surface of thelaminate and a second prepreg layer to the lower surface of thelaminate.